1. Field of the Invention
The present invention relates to a device for supplying high-pressure fuel to an internal combustion engine. More particularly, the invention relates to a high-pressure fuel supply device which regulates the amount of fuel to be supplied to an internal combustion engine with a fuel spill valve.
2. Description of the Related Art
A device for supplying high-pressure fuel to an internal combustion engine generally includes a pressure chamber which pressurizes fuel to be supplied to the internal combustion engine and a spill valve which regulates the amount of fuel to be supplied to the internal combustion engine by changing the amount of fuel spilling from the pressure chamber (see, for example, Japanese Laid-Open Publication No. 2-146256 titled "Variable discharge high-pressure pump").
FIG. 7 shows an example of such a conventional high-pressure fuel supply device. Referring to FIG. 7, a high-pressure fuel supply device 100 includes a cylinder 101, a plunger 102 disposed in the cylinder 101 so as to reciprocate therein, and a plunger chamber 103 defined by the cylinder 101 and the plunger 102. The plunger 102 moves upward and downward in response to the rotation of a crank shaft (not shown) of an internal combustion engine 115.
A spill passage 104 which is open to the plunger chamber 103 is formed in the cylinder 101. An opening 104a of the spill passage 104 is opened and closed by a valve body 105a of a solenoid valve 105 disposed on the cylinder 101 (shown in the upper part of FIG. 7). The activation of the solenoid valve 105 is controlled by an electronic control device (not shown) of the internal combustion engine 115.
The spill passage 104 is associated with a fuel tank 109 via an introduction bore 106, a fuel reservoir 107, and a supply pump 108. The supply pump 108 pumps fuel out from the fuel tank 109 toward the plunger chamber 103. The plunger chamber 103 is also associated with a common rail 112 via a high-pressure fuel passage 110 provided with a check valve 111. The common rail 112 is provided with a plurality of injectors 113 corresponding to respective cylinders of the internal combustion engine 115, so that fuel in the common rail 112 is injected from the injectors 113 into combustion chambers of the corresponding cylinders.
The fuel reservoir 107 is also associated with the fuel tank 109 via a relief passage 116. The relief passage 116 is provided with a pressure adjusting valve 117. When the pressure of the fuel in the fuel reservoir 107 increases to a predetermined value or more, the pressure adjusting valve 117 opens to allow fuel in the fuel reservoir 107 to flow back to the fuel tank 109.
In the device 100 with the above configuration, when the plunger 102 moves downward in the cylinder 101 while the solenoid valve 105 is open, fuel pumped by the supply pump 108 is allowed to enter the plunger chamber 103 via the spill passage 104. In the case where the solenoid valve 105 is kept open, as the plunger 102 moves upward, the fuel in the plunger chamber 103 spills therefrom to flow back to the fuel reservoir 107 via the spill passage 104 and the like. In this case, therefore, the fuel in the plunger chamber 103 is not pressurized.
On the contrary, in the case where the solenoid valve 105 is closed after the fuel is introduced into the plunger chamber 103, the fuel is pressurized as the plunger 102 moves upward. When the pressure of the fuel in the plunger chamber 103 increases to a predetermined value at which the check valve 111 opens or more, the check valve 111 opens to allow the fuel to be pressed to flow into the common rail 112 via the high-pressure fuel passage 110.
In the device 100 with the above operation, the amount of fuel pressed to flow from the plunger chamber 103 to the common rail 112 can be regulated by changing the time when the solenoid valve 105 is closed. For example, when the solenoid valve 105 is closed simultaneously with the start of the upward movement of the plunger 102, all the fuel existing in the plunger chamber 103 is pressurized and discharged, resulting in the maximum fuel discharge amount from the device to the common rail 112. On the contrary, when the solenoid valve 105 is kept open even after the start of the upward movement of the plunger 102, part of the fuel existing in the plunger chamber 103 spills out to the spill passage 104 to be returned to the fuel tank 109. Then, by closing the solenoid valve 105 during the upward movement of the plunger 102, the remaining fuel in the plunger chamber 103 is pressurized and discharged to the common rail 112. In other words, the fuel discharge amount can be regulated by controlling the duration from the start of the upward movement of the plunger 102 until the time when the solenoid valve 105 is closed.
Alternatively, the solenoid valve 105 may be closed simultaneously with the start of the upward movement of the plunger 102 and then opened during the upward movement of the plunger 102. By changing the time when the solenoid valve 105 is opened, the fuel discharge amount can be changed.
The device 100 therefore makes it possible to keep the pressure of the fuel in the common rail 112 at a predetermined value by changing the time when the solenoid valve 105 is opened or closed so as to change the fuel discharge amount.
However, the above high-pressure supply device 100 has the following problems. When fuel in the plunger chamber 103 is to be pressurized, the solenoid valve 105 needs to be in the closed state in response to a close signal from the electronic control device. However, a response lag exists from the time when the close signal is output from the electronic control device until the time when the solenoid valve 105 has actually been closed. In the case of securing the maximum discharge amount from the device 100, therefore, the close signal must be output to the solenoid valve 105 earlier in consideration of this response lag, so as to ensure that the solenoid valve 105 has been closed when the plunger 102 starts moving upward. If the solenoid valve 105 has not been closed when the plunger 102 is moving upward from the bottom dead center, the fuel in the plunger chamber 103 will spill out via the spill passage 104.
In order to accomplish the above, the solenoid valve 105 should be closed before the plunger 102 reaches the bottom dead center. In this case, however, the spill passage 104 starts closing while fuel should still be introduced into the plunger chamber 103 via the spill passage 104. As a result, the conventional device 100 fails to introduce into the plunger chamber 103 a sufficient amount of fuel required to obtain the maximum discharge amount, thereby lowering the fuel discharge capability of the device.
Accordingly, for the conventional device 100, it is difficult to rapidly increase the fuel pressure in the common rail 112 at the start of the internal combustion engine 115, at which the fuel pressure in the common rail 112 should be rapidly increased to a predetermined value by maximizing the discharge amount of the device 100.
At high-load operation of the internal combustion engine 115, the speed of the reciprocation of the plunger 102 increases, and thus the ratio of the response lag time to the time required to introduce fuel into the plunger chamber 103 and pressurize it therein becomes comparatively large. As a result, the conventional device 100 may fail to secure a sufficient discharge amount required to meet the increase in the fuel amount injected from the injectors 113, and thus the fuel in the common rail 112 may not be kept at a predetermined pressure.
In view of the foregoing, the objective of the present invention is to provide a high-pressure fuel supply device for an internal combustion engine which has improved fuel supply capability.